1. Field of the Invention
This invention relates to the detection of dimethylaluminumhydride (DMAH) and equipment useful for such detection. More particularly, the invention relates to an apparatus and method for detecting DMAH using a particle detecting apparatus, specifically, and ionization-type detector.
2. Background of the Related Art
The processing of semiconductor wafers often requires the formation of thin films of material. These thin films are often formed utilizing Chemical Vapor Deposition (CVD) techniques that sometimes require the use of materials that are in their liquid phase at room temperature. One such material is DMAH which serves as a source for aluminum in the production of thin films.
To introduce DMAH into a CVD reaction vessel, the liquid material is charged in a bubbler. A carrier gas is introduced through a nozzle immersed within the liquid in the bubbler at a rate controlled by a mass-flow controller. This generates bubbles of the carrier gas within the DMAH liquid which ascend through the liquid. As a result, the DMAH is vaporized into and becomes mixed with the carrier gas. The carrier gas containing the DMAH vapor is then introduced into the reaction vessel for subsequent deposition onto the substrate to form a thin film. Accordingly, any leaks in the vessel and related delivery lines will allow the DMAH vapor to escape. As DMAH is pyrophoric, any leak must be immediately detected. However, without adequate detection apparatus, DMAH cannot be used for the commercial production of film layers because of the fire risk it presents. Known techniques for detecting DMAH include gas chromatography, which examines a sample of the gas for its constituents, and provides a "signature" of the gas. This signature is then compared, typically manually, to a known DMAH signature, to determine the presence of DMAH. This detection method is expensive, time consuming, and somewhat operator dependant. Where leakage of a pyrophoric gas such as DMAH is to be detected, this method is unacceptable in a manufacturing environment, because unacceptable quantities of gas would leak before detection of the leak occurs. This need for detection of gas leakage is equally applicable to other gases, particularly other pyrophoric gases used in manufacturing processes.
Presently though, there are no known devices to detect gaseous DMAH which has escaped from the DMAH delivery system.